1. Field of Invention
This invention is related to the oxidation of olefins to their corresponding olefin oxides and ketones and, in particular, is related to the oxidation of propylene by thallic oxide in an aqueous, CO.sub.2 rich environment.
2. Description of Prior Art
W. Kruse, et al, J. Org. Chem. 30th Vol., pp. 114 ('71) describes the preparation of certain selected epoxides by the oxidation of the corresponding olefin with thallic acetate in weakly solvating media.
U.S. Pat. No. 3,641,067 (issued in 1972 to W. Kruse) also describes the preparation of the epoxide of propylene and isobutylene in an aqueous system by using lower alkyl thallic carboxylates, in the presence of a water-miscible organic solvent and an aliphatic monocarboxylic acid containing from one to four carbon atoms.
French Pat. No. 2,255,298 (issued in 1975 to Societe des Usines Chimiques Rhone-Poulenc) sought to improve the concentration of propylene oxide in the product by a multi-step process of reacting propylene at low temperatures with an aqueous solution having a pH of not greater than six and containing a thallic salt of an aliphatic monocarboxylic acid having from one to four carbon atoms, a carboxylic acid which is miscible with or soluble in water, and a water-miscible organic solvent. (Aliphatic monocarboxylic acids of one to four carbon atoms are specified as being suitable.) The pH of the resulting reaction mixture is next critically adjusted to a value of at least seven and the adjusted solution then heated, with immediate and rapid removal of the propylene oxide formed.
While French Pat. No. 2,255,298 achieves effective results, the careful pH control required in this process is quite costly on an industrial scale.
U.S. Pat. No. 4,021,453 to W. F. Brill discloses a process for preparing epoxides from the corresponding olefins using aryl thallic carboxylates having up to 12 carbon atoms in the presence of an inert polar organic solvent and water and, optionally, in the presence of free aryl carboxylic acids.
U.S. Pat. No. 4,290,959 to R. S. Barker discloses a process for preparing propylene oxide in which propylene is oxidized by means of a thallic salt in the presence of aqueous media containing an alkanoic acid having at least seven carbon atoms and, optionally, in the presence of an organic solvent.
U.S. Pat. Nos. 4,031,196 and 4,146,545 to J. Leonard disclose the use of thallic oxide in the preparation of propylene oxide. In an aqueous alkaline solution having a pH greater than 11.9, thallous isobutyrate is oxidized by air at a temperature within a range from about 90.degree. to about 250.degree. C. to prepare a slurry of thallic oxide from which thallic oxide can be recovered. The alkaline isobutyrate solution can be treated with carbon dioxide under pressure to form an isobutyric acid product which can be solvent extracted from the aqueous system using a hydrophobic solvent as extractant. Gaseous propylene can be bubbled through a liquid reaction mixture containing water, an organic solvent miscible with water and thallic trialkanoate to prepare gaseous propylene oxide. The carbonate salt can be thermally decomposed to regenerate an alkaline metal hydroxide and carbon dioxide. The availability of this preparation of thallic oxide makes feasible the recycling of most of the reaction components. This process is extremely awkward, however, particularly on a large industrial scale, involving many separate operations.
Oxidation of thallous compounds to the thallic state is well known and has been disclosed in a great number of publications and patents. A substantial number of these are disclosed in U.S. Pat. No. 4,192,814.
There has been a long standing need to discover an efficient, economical, process which uses thallic values for the oxidation of olefinic compounds to their corresponding oxides while permitting the efficient and effective back oxidation and recycling of the reduced thallous values to their thallic state for reuse in the process cycle.
It is an object of this invention to provide an improved cyclical process for the oxidation of olefins to their corresponding olefin oxides and ketones by the use of thallic oxide as the oxidizing agent in an organic solvent-free, acid-free medium.
It is another object of this invention to provide an improved olefin oxidizing process which employs thallic oxides as the oxidizing agent that can efficiently and economically subsequently regenerate the thallous values back to the thallic state after the reduction in the olefin oxidizing reaction.
It is still another object of this invention to remove the oxidized olefin products from the reaction mixture without having any significant glycol formation.
It is still another object of the invention to develop a thallous oxidizing catalyst which is compatible with the formed olefin products of the process.
It is still another object of this invention to develop a more catalytically active thallic oxide than those currently commercially available for use in the oxidation reaction.
These and other objects, aspects and advantages of this invention will be apparent to those skilled in the art from the following description.